Japan's Kei Nishikori battled through a second challenging three-set test on Thursday to reach an ATP Washington Open quarter-final against a foe he has never beaten, Frenchman Richard Gasquet.
Fourth-seeded Nishikori outlasted Slovakian Lukas Lacko 6-2, 2-6, 6-3 while sixth seed Gasquet downed American Tim Smyczek 6-3, 6-2.
That will send two of the three top remaining seeds in the $1.9 million (€1.4 million) hardcourt event against each other to decide a semi-final berth.
"I'm sure it's going to be the toughest match this week," Nishikori said. "I've never beaten him so it's going to be a big challenge."
Gasquet, ranked 14th is 4-0 all-time against 11th-ranked Nishikori, having dropped only one set to him. But this will be the nearest to a final they have met.
Gasquet won their first meeting at Tokyo in 2008, again at Queen's in 2010 and twice last year at Montreal and Paris ATP Masters series events.
"He has a great serve, strong forehand and backhand and he's very talented," Nishikori said. "I have to serve better than I did today."
Nishikori fired eight aces but made six double faults and connected on only 53% of his first serves against Lacko.
"It was tough," Nishikori said. "The second set he began playing much better. Maybe I lost concentration but I fought through it in the third set."
Nishikori jumped ahead 4-0 before Lacko won the next three games only to have Nishikori raise his game and break him to claim the match, his second three-set triumph in a row.
"It's a positive for me to win in three sets two matches in a row," Nishikori said, noting that he wanted matches to build confidence after a three-week layoff since Wimbledon.
Nishikori, 24, is seeking his sixth career ATP title and third of the season after defending a crown at Memphis and collecting a clay-court title at Barcelona. He also won in 2008 at Delray Beach and at Tokyo in 2012.
Gasquet, 28, seeks his 11th career ATP crown and first on US soil after taking titles last year at Doha, Moscow and Montpelier, where he was runner-up this year. He was also a finalist at Eastbourne this season.
Gasquet, who made a semi-final run at last year's US Open to match his best Grand Slam showing from Wimbledon in 2007, played two weeks ago at Bogota and suffered a right arm injury that forced him out of last week's event in Atlanta.
"I couldn't even serve a ball," Gasquet said. "For three days here I didn't serve. Now it feels fine."
That gives him hope of duplicating his success in Flushing Meadows when the US Open begins on August 25.
"There are a lot of big matches to come for me," Gasquet said.